[PATCH] platform/x86: dell-ddv: Fix taking the psy->extensions_sem lock twice

[Hans de Goede <hansg@kernel.org>]

dell_wmi_ddv_get_property() gets called with psy->extensions_sem
read-locked, it calls dell_wmi_ddv_battery_translate() which calls
power_supply_get_property() on the same psy which again read-locks
psy->extensions_sem.

Lockdep rightfully complains about this:

 ============================================
 WARNING: possible recursive locking detected
...
 kworker/16:3/1230 is trying to acquire lock:
 ffff8c3143417658 (&psy->extensions_sem){++++}-{4:4},
  at: power_supply_get_property.part.0+0x23/0x160
 but task is already holding lock:
 ffff8c3143417658 (&psy->extensions_sem){++++}-{4:4},
  at: power_supply_get_property.part.0+0x23/0x160
...
  Possible unsafe locking scenario:

        CPU0
        ----
   lock(&psy->extensions_sem);
   lock(&psy->extensions_sem);

  *** DEADLOCK ***
...
 Call Trace:
  <TASK>
  ...
  down_read+0x3e/0x180
  ? power_supply_get_property.part.0+0x23/0x160
  power_supply_get_property.part.0+0x23/0x160
  dell_wmi_ddv_battery_translate+0x68/0x1d0 [dell_wmi_ddv]
  ? lock_acquire+0xd9/0x2c0
  dell_wmi_ddv_get_property+0x25/0x240 [dell_wmi_ddv]
  power_supply_get_property.part.0+0x87/0x160
  power_supply_format_property+0xc4/0x3d0
  add_prop_uevent+0x26/0x90
  power_supply_uevent+0xb9/0xf0

This usually works fine, because read-locking can be done multiple times
but if someone tries to write-lock between the 2 read-lock calls then
the second read-lock will block on the write-lock and the write-lock will
be blocked on the first read-lock leading to a deadlock.

The serial is part of the main psy device, not of an extension. Directly
call psy->desc->get_property() in dell_wmi_ddv_battery_translate() to fix
the double-lock issue.

Note this also influences eppid_show() which is called directly rather
then through power_supply_get_property(). This is ok since the ACPI
battery is fully ready to be used when the battery hook's add_battery
callback is called.

Fixes: 058de163a376 ("platform/x86: dell-ddv: Implement the battery matching algorithm")
Signed-off-by: Hans de Goede <hansg@kernel.org>
---
 drivers/platform/x86/dell/dell-wmi-ddv.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/platform/x86/dell/dell-wmi-ddv.c b/drivers/platform/x86/dell/dell-wmi-ddv.c
index 67f3d7158403..95cc3139f271 100644
--- a/drivers/platform/x86/dell/dell-wmi-ddv.c
+++ b/drivers/platform/x86/dell/dell-wmi-ddv.c
@@ -689,9 +689,11 @@ static int dell_wmi_ddv_battery_translate(struct dell_wmi_ddv_data *data,
 
 	dev_dbg(&data->wdev->dev, "Translation cache miss\n");
 
-	/* Perform a translation between a ACPI battery and a battery index */
-
-	ret = power_supply_get_property(battery, POWER_SUPPLY_PROP_SERIAL_NUMBER, &val);
+	/*
+	 * Perform a translation between a ACPI battery and a battery index. Directly call
+	 * desc->get_property() to avoid locking battery->extensions_sem a second time.
+	 */
+	ret = battery->desc->get_property(battery, POWER_SUPPLY_PROP_SERIAL_NUMBER, &val);
 	if (ret < 0)
 		return ret;
 
-- 
2.49.0